/*
 * Copyright 2011 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.web.bindery.event.shared;

import com.google.web.bindery.event.shared.Event.Type;

import java.util.*;

/**
 * Basic implementation of {@link EventBus}.
 */
public class SimpleEventBus extends EventBus {
	private final boolean isReverseOrder;
	/**
	 * Map of event datyType to map of event source to list of their handlers.
	 */
	private final Map<Event.Type<?>, Map<Object, List<?>>> map = new HashMap<Event.Type<?>, Map<Object, List<?>>>();
	private int firingDepth = 0;

	/**
	 * Add and remove operations received during dispatch.
	 */
	private List<Command> deferredDeltas;

	public SimpleEventBus() {
		this(false);
	}

	/**
	 * Allows creation of an instance that fires its handlers in the reverse of
	 * the order in which they were added, although filtered handlers all fire
	 * before unfiltered handlers.
	 * <p>
	 *
	 * @deprecated This is a legacy feature, required by GWT's old
	 *             HandlerManager. Reverse order is not honored for handlers
	 *             tied to a specific event source (via
	 *             {@link #addHandlerToSource}.
	 */
	@Deprecated
	protected SimpleEventBus(boolean fireInReverseOrder) {
		isReverseOrder = fireInReverseOrder;
	}

	@Override
	public <H> HandlerRegistration addHandler(Type<H> type, H handler) {
		return doAdd(type, null, handler);
	}

	@Override
	public <H> HandlerRegistration addHandlerToSource(final Event.Type<H> type, final Object source, final H handler) {
		if (source == null) {
			throw new NullPointerException("Cannot add a handler with a null source");
		}

		return doAdd(type, source, handler);
	}

	@Override
	public void fireEvent(Event<?> event) {
		doFire(event, null);
	}

	@Override
	public void fireEventFromSource(Event<?> event, Object source) {
		if (source == null) {
			throw new NullPointerException("Cannot fire from a null source");
		}
		doFire(event, source);
	}

	/**
	 * @deprecated required by legacy features in GWT's old HandlerManager
	 */
	@Deprecated
	protected <H> void doRemove(Event.Type<H> type, Object source, H handler) {
		if (firingDepth > 0) {
			enqueueRemove(type, source, handler);
		} else {
			doRemoveNow(type, source, handler);
		}
	}

	/**
	 * @deprecated required by legacy features in GWT's old HandlerManager
	 */
	@Deprecated
	protected <H> H getHandler(Event.Type<H> type, int index) {
		assert index < getHandlerCount(type) : "handlers for " + type.getClass() + " have size: " + getHandlerCount(type) + " so do not have a handler at index: " + index;

		List<H> l = getHandlerList(type, null);
		return l.get(index);
	}

	/**
	 * @deprecated required by legacy features in GWT's old HandlerManager
	 */
	@Deprecated
	protected int getHandlerCount(Event.Type<?> eventKey) {
		return getHandlerList(eventKey, null).size();
	}

	/**
	 * @deprecated required by legacy features in GWT's old HandlerManager
	 */
	@Deprecated
	protected boolean isEventHandled(Event.Type<?> eventKey) {
		return map.containsKey(eventKey);
	}

	private void defer(Command command) {
		if (deferredDeltas == null) {
			deferredDeltas = new ArrayList<Command>();
		}
		deferredDeltas.add(command);
	}

	private <H> HandlerRegistration doAdd(final Event.Type<H> type, final Object source, final H handler) {
		if (type == null) {
			throw new NullPointerException("Cannot add a handler with a null datyType");
		}
		if (handler == null) {
			throw new NullPointerException("Cannot add a null handler");
		}

		if (firingDepth > 0) {
			enqueueAdd(type, source, handler);
		} else {
			doAddNow(type, source, handler);
		}

		return new HandlerRegistration() {
			public void removeHandler() {
				doRemove(type, source, handler);
			}
		};
	}

	private <H> void doAddNow(Event.Type<H> type, Object source, H handler) {
		List<H> l = ensureHandlerList(type, source);
		l.add(handler);
	}

	private <H> void doFire(Event<H> event, Object source) {
		if (event == null) {
			throw new NullPointerException("Cannot fire null event");
		}
		try {
			firingDepth++;

			if (source != null) {
				setSourceOfEvent(event, source);
			}

			List<H> handlers = getDispatchList(event.getAssociatedType(), source);
			Set<Throwable> causes = null;

			ListIterator<H> it = isReverseOrder ? handlers.listIterator(handlers.size()) : handlers.listIterator();
			while (isReverseOrder ? it.hasPrevious() : it.hasNext()) {
				H handler = isReverseOrder ? it.previous() : it.next();

				try {
					dispatchEvent(event, handler);
				} catch (Throwable e) {
					if (causes == null) {
						causes = new HashSet<Throwable>();
					}
					causes.add(e);
				}
			}

			if (causes != null) {
				throw new UmbrellaException(causes);
			}
		} finally {
			firingDepth--;
			if (firingDepth == 0) {
				handleQueuedAddsAndRemoves();
			}
		}
	}

	private <H> void doRemoveNow(Event.Type<H> type, Object source, H handler) {
		List<H> l = getHandlerList(type, source);

		boolean removed = l.remove(handler);

		if (removed && l.isEmpty()) {
			prune(type, source);
		}
	}

	private <H> void enqueueAdd(final Event.Type<H> type, final Object source, final H handler) {
		defer(new Command() {
			public void execute() {
				doAddNow(type, source, handler);
			}
		});
	}

	private <H> void enqueueRemove(final Event.Type<H> type, final Object source, final H handler) {
		defer(new Command() {
			public void execute() {
				doRemoveNow(type, source, handler);
			}
		});
	}

	private <H> List<H> ensureHandlerList(Event.Type<H> type, Object source) {
		Map<Object, List<?>> sourceMap = map.get(type);
		if (sourceMap == null) {
			sourceMap = new HashMap<Object, List<?>>();
			map.put(type, sourceMap);
		}

		// safe, we control the puts.
		@SuppressWarnings("unchecked")
		List<H> handlers = (List<H>) sourceMap.get(source);
		if (handlers == null) {
			handlers = new ArrayList<H>();
			sourceMap.put(source, handlers);
		}

		return handlers;
	}

	private <H> List<H> getDispatchList(Event.Type<H> type, Object source) {
		List<H> directHandlers = getHandlerList(type, source);
		if (source == null) {
			return directHandlers;
		}

		List<H> globalHandlers = getHandlerList(type, null);

		List<H> rtn = new ArrayList<H>(directHandlers);
		rtn.addAll(globalHandlers);
		return rtn;
	}

	private <H> List<H> getHandlerList(Event.Type<H> type, Object source) {
		Map<Object, List<?>> sourceMap = map.get(type);
		if (sourceMap == null) {
			return Collections.emptyList();
		}

		// safe, we control the puts.
		@SuppressWarnings("unchecked")
		List<H> handlers = (List<H>) sourceMap.get(source);
		if (handlers == null) {
			return Collections.emptyList();
		}

		return handlers;
	}

	private void handleQueuedAddsAndRemoves() {
		if (deferredDeltas != null) {
			try {
				for (Command c : deferredDeltas) {
					c.execute();
				}
			} finally {
				deferredDeltas = null;
			}
		}
	}

	private void prune(Event.Type<?> type, Object source) {
		Map<Object, List<?>> sourceMap = map.get(type);

		List<?> pruned = sourceMap.remove(source);

		assert pruned != null : "Can't prune what wasn't there";
		assert pruned.isEmpty() : "Pruned unempty list!";

		if (sourceMap.isEmpty()) {
			map.remove(type);
		}
	}

	private interface Command {
		void execute();
	}
}